After speaking to Malene, travel to the cave. Soon after entering, the Hero will encounter Ghosts or Wraiths depending on level. To reach Raelynn, who is in the last room deep in the cave, they have to pass several rooms with necromancers, usually one or two in each area, and they will summon their associated undead. There are also a few chests around the cave.

The door to the room Raelynn is in has a hard lock, either lockpick it to open or get the key from one of the necromancers. In her room she has an altar and 2 chests with various loot. On the altar are some gemstones. When the Hero have killed Raelyn, head back to the Roxey Inn to collect the reward from Malene.

Malene at the Roxey Inn in the wilderness north of the Imperial City has asked me to help her rid the area of a Necromancer who calls herself Raelynn the Gravefinder. Raelynn can be found in Moss Rock Cavern to the north.

Update: After killing Raelynn:

I've slain Raelynn the Gravefinder. I should return to Malene at the Roxey Inn and deliver the good news.

Update: Upon speaking to Malene again:

Malene was delighted with the news of Raelynn the Gravefinder's death, and rewarded me with some coin (sic).